The adsorptive capacity of charcoal has been documented since
the time of Hippocrates and has been known for centuries. Two independent
researchers were responsible for its wide acceptance in the early
nineteenth century when each of them performed a demonstration of
its effectiveness by ingesting lethal doses of strychnine and arsenic,
respectively, followed by charcoal. Both of them survived. The twentieth
century has seen charcoal come into wide medical use as further investigation
showed its effectiveness to adsorb a wide variety of compounds.1
Charcoal is produced by the distillation of the pyrolysis products
of vegetable matter or wood. It works by directly adsorbing toxins
via a variety of chemical binding properties and thereby preventing
the toxins from being absorbed from the gastrointestinal tract.
Improvement in the adsorptive capability of charcoal is achieved
by heating it to a temperature of 900 Celsius and washing it in
a stream of carbon dioxide gas or steam. This process is called
activation and creates an internal pore structure that increases
the surface area from 2 to 4 square meters per gram to greater than
2000 square meters per gram.2 A typical dose of 50 grams
of activated charcoal has the surface area of ten football fields.
Charcoal is not absorbed from the intestinal lumen and is not modified
by the numerous enzymes and proteins that aid in the digestion
of food. It passes through the intestinal tract and is
expelled from the anus as a sticky black substance.
Some charcoal preparations contain sorbitol. This substance is
used as a flavoring agent to make food, drinks, and medications
more palatable. Sorbitol is also used as a hyperosmotic laxative agent.
It is poorly absorbed from the gastrointestinal tract and converted
into fructose by the liver. Its limited absorption into the body
results in an increased volume of water secreted into the intestine
and an increased intraluminal pressure stimulating a catharsis.
A second mechanism of charcoal’s action involves the
patient’s enteroenteral and enterohepatic circulation.
A diffusion gradient is created in the intestine due to the huge
adsorptive ability of charcoal to bind free drug or free toxin.
This makes the toxin concentration in the intestine effectively
zero. The intestinal wall works as a semipermeable membrane allowing
the drug or toxin to diffuse from the capillaries into the lumen
of the intestine. The charcoal cannot cross the wall of the intestine
and is not absorbed. This diffusion gradient draws the drug or toxin
into the intestine and allows the activated charcoal to trap it,
maintaining the gradient.3 This mechanism essentially dialyzes
the blood in the capillaries of the intestinal circulation. Many
drugs, toxins, and their metabolites are secreted into the bile
and back into the intestinal lumen. Activated charcoal will adsorb
these substances and prevent them from once again entering the systemic
Activated charcoal is effective for the majority of commonly
ingested substances and is considered the agent of ...